Grease-proof paper



United States Patent GREASE-PROOF PAPER Donald K. Pattilloch, New York, and Carl Polowczyk,

Elmhnrst, N.Y., assignors to Michigan Research Laboratories, Inc., Long Island City, N.Y., a corporation of Michigan, and Electro-Chem Fiber Seal Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed May 1, 1957, Ser. No. 656,220

7 Claims. (Cl. 162-157) This invention relates to grease-proof paper, particularly paper containing perfluoroalkanoic acids as greaseproofing agent.

Perfluoroalkanoic acids, in an insoluble form, as in complexes, are known to form grease-proof coating on paper. The prior art methods involve coating or impregnation of paper with water-insoluble complexes of the acids. In order to impregnate the paper with sufficient grease-proofing agent, the paper base must be sufficiently porous to take up the agent. Such porous paper is inferior for many applications where a dense, compact sheet is required. Prior art coatings have also required an uneconomical amount of grease-proofing agent.

The present invention overcomes the disadvantages of the prior art by yielding a dense, compact paper containing an ellective amount of grease-proofing agent. The process of the present invention involves reacting cellulose fibers while suspended in an aqueous medium with polyethylene imine, reacting the resulting reaction product with a perfluoroalkanoic acid and forming the suspension into a sheet.

The grease-proof paper thus has the active agent linked to the cellulose fibers as distinct from impregnated in or coated thereon, and the sheet can be formed to any desired compactness by the usual paper making procedures.

The perfluoroalkanoic acids useful in the present invention are those having from 4 to carbon atoms and having the formula c r coorl where n is from 3 to 9. The acids include heptafluorobutyric acid, undecaflnorocaproic acid and pentadecafluorooctanoic acid, for example. They are most conveniently referred to as perfiuorobutyric acid, perfluorohexanoic acid and perfluorooctanoic acid, respectively.

The acids per se or their water-insoluble complexes may be used, such as the complexes with chromyl chloride.

Polyethylene imine reacts with the hydroxyl or carboxyl groups of cellulose and the reactive amino hydrogen apparently reacts with the perfluoroalkanoic acid through the carboxyl group to chemically link the agent to the cellulose and imparts the desired properties to the cellulosic sheet.

Example I Bleachedlkraft pulp was defibered and beaten to a Canadian standard freeness of 250. A 10% by weight aqueous soliition of polyethylene imine having a molecular weight of about 30,000 was added to the pulp in the beater in an amount of 0.5% polyethylene imine by weight of the dry weight of the pulp and beating continued for one-half hour, to permit complete reaction. Thereafter perfluorooctanoic acid in ammoniacal water solution was added to the heater in an amount of 0.5% perfluorooctanoic acid by weight of the dry fiber. The uspension was then adjusted to pH 4 with formic acid ice and beating continued for one hour. Hand sheets were formed in customary manner and dried at a drier face temperature of about 240 F. The resulting sheets, 2.5 mils thick, 30 pound weight, withstood penetration by corn oil for 48 hours at l30l60 F. Ordinary untreated kraft sheets of the same Weight were instantaneously penetrated by corn oil at room temperature.

Example II Bleached kraft pulp was defibered and beaten to Canadian standard freeness of 400. Polyethylene imine in an amount of 0.5 by weight of the dry pulp was added as in Example I and beating continued for onehalf hour. One-half percent by weight of per-fluorooctanoic acid-chromyl chloride complex in isopropanol solution was added; the pH adjusted to pH 3.5 with formic acid, and beating of the suspension was continued for one hour. Hand sheets were formed and dried. Six mil, 70 pound sheets resisted penetration by corn oil for 45 hours at room temperature.

It has been found that the reaction of polyethylene imine with cellulose pulp is quantitative; that is, essentially no polyethylene imine appears in the white water. Likewise, essentially no perfluoroalkanoic acid appears in the white water, indicating complete reaction. For effective grease-proofing, it has been found that about 0.25 to 1% by weight of polyethylene imine and about 0.25% to 2% by weight of the perfluoroalkanoic acid may be used.

The process is suited to usual paper making techniques, including operations on Fourdrinier and cylinder machines. Multicyclinder board machines may be used to form board, especially board containing one or more plies of grease-proof stock and one or more plies of waterproof stock, thereby forming a composite board impervious to both grease and water. A suitable water-proof stock, includes for example, a pulp stock which has been treated with a polyfunctional cationically active activating agent and thereafter reacted with an ammonium rosin complex containing essentially no hydrophilic ions, and after such reaction, the pH value of the so-treated stock is adjusted to between pH 4.2 and pH 5.2 by the additions of a suitable amount of a water soluble salt of a polyvalent metallic ion.

Example III Perfluorooetanoic acid-reacted pulp as prepared in Example I was delivered to the top liner vat of an 8-cylinder board machine. The filler vats contained unbleached kraft pulp having 450 Canadian standard freeness. The bottom liner vat contained a waterproofing pulp prepared as follows:

To bleached, defibered kraft pulp (Canadian standard freeness 400) was added 0.5% by weight (on dry pulp basis) of an aqueous dispersion of dicyandiamide-formaldehyde reaction product, a polyfunctional cationically reactive fiber activator, and beating for one-half hour continued. Thereafter 4% on dry solids basis, of rosin ammonium complex (prepared by refluxing 4 parts rosin with 3 parts 26 B. ammonia in methanol for 6 hours) was added in the form of a 10% water suspension and beating continued for twenty minutes.

The resulting 8-ply board, after drying, exhibited excellent grease resistance on the perfluorooctanoic acid side and excellent resistance to boiling water on the waterproof side.

It is apparent that board of any desired number of plies may be prepared, including two-ply, consisting solely of the grease-proof and waterproof sheets. It is also apparent that any desired water-proofing material may be employed.

Polyethylene imine, or polymerized ethyleneimine, has

a molecular weight of about 30,000 to 40,000 and has the formula HBOw-CHB where n is about 700 to 800.

The process of the present invention is operable with all types of cellulose pulp, including, sulfite, soda, kraft, rag, mechanical and semichemical pulps, both bleached and unbleached.

While the invention has been described in terms of certain examples, such examples are to be considered illustrative rather than limiting, and it is intended to cover all modifications and embodiments that fall within the spirit and scope of the appended claims.

What is claimed is:

1. The process of producing grease-proof paper comprising reacting cellulose fibers while suspended in an aqueous medium with polyethylene imine, reacting the resulting reaction product with a perfluoroalkanoic acid containing from 4 to 10 carbon atoms and forming the suspension into a sheet.

2. The process set forth in claim 1 wherein about 0.25% to 1% polyethylene imine and about 0.25% to 4 2% perfluoroalkanoic acid by weight of the dry cellulose fibers is employed.

3. The process set forth in claim 1 wherein the perfluoroalkanoic acid is perfluorooctanoic acid.

4. The process set forth in claim 1 wherein the perfluoroalkanoic acid is a complex of perfluorooctanoic acid and chromyl chloride.

5. Grease-proof paper, the individual fibers of which comprise cellulose fibers reacted with polyethylene imine and subsequently reacted with a perfluoroalkanoic acid containing 4 to 10 carbon atoms.

6. Paper set forth in claim 5 wherein the perfluoroalkanoic acid is perfluorooctanoic acid.

7. Paper set forth in claim 5 wherein the perfluoroalkanoic acid is a complex of perfluorooctanoic acid and chromyl chloride.

References Cited in the file of this patent UNITED STATES PATENTS 1,606,428 Kirschbraun Nov. 9, 1926 1,995,145 Frost Mar. 19, 1935 2,662,835 Reid Dec. 15, 1953 2,698,793 Landes et al Jan. 4, 1955 

1. THE PROCESS OF PRODUCING GREASE-PROOF PAPER COMPRISING REACTING CELLULOSE FIBERS WHILE SUSPENDED IN AN AQUEOUS MEDIUM WITH POLYETHYLENE IMINE, REACTING THE RESULTING REACTION PRODUCT WITH A PERFLUOROALKANOIC ACID CONTAINING FROM 4 TO 10 CARBON ATOMS AND FORMING THE SUSPENSION INTO A SHEET. 